First amp build completed

Discussion in 'Amp Tech Center' started by 8urchevy, Feb 14, 2019.

  1. 8urchevy

    8urchevy Tele-Meister

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    Hello, I have finished the wiring of my first amp build which is a Bassman.5f6a circuit. I used a old Bogen pa complete with original tubes. The pt doesn't have a bias tap so I cathode biased it .It works, but I need to switch my connections on the treble pot as it works backwards.

    What file format do I need to use to upload a sound sample?

    The clean tones I am happy with, but the breakup is terrible. I haven't put the other half of v1 in circuit yet and probably will add it in on a switch. Here is a snapshot of the guts. Any advice is greatly appreciated . Thank you
    0124191014a.jpg
     
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  2. robrob

    robrob Poster Extraordinaire Ad Free Member

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  3. 8urchevy

    8urchevy Tele-Meister

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    Thank you. I agree and will look into that. Do you see anything I may have done wrong or should have done differently? By terrible break up I am talking more of playing lead lines. It sounds a bit anemic to me even cranked up at max volume. I don't have a tube tester and the tubes are original from 1961 with evidence of being well used so perhaps a new set of output tubes is in order. It has great rock crunch but the lead tones are not quite singing. I am going to add the other half of v1 and that should liven things up I reckon.

    There is also a constant hum with or without a guitar plugged in and I used the switched jack. It isn't overpowering while playing, but still annoying.

    How do I upload a sound sample? It won't let me upload the file which is an mp3.

    THank you for your time.
     
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  4. Whatizitman

    Whatizitman Friend of Leo's

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    I think you have to use something like SoundCloud, and link to it. Easiest to record a phone video and put it in YouTube and link to it. Or if you make a nice audio recording, use SoundCloud.
     
  5. 8urchevy

    8urchevy Tele-Meister

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    First part is clean tones and second half is gain turned up. Played on a LP through a 212 cab. Master volume isn't very loud, but even cranked up to max the same results happen. It sounds too tight. No "edge of break up" to be found and that is where I like to live.
     
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  6. Luthier Vandros

    Luthier Vandros Tele-Holic

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    The lead dress could be suspect. Parasitic oscillations can cause some of the troubles you’re experiencing.
     
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  7. 8urchevy

    8urchevy Tele-Meister

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    Is there a particular area in my build that looks suspect to you? Thanks for the reply.
     
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  8. Luthier Vandros

    Luthier Vandros Tele-Holic

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    I don’t have time to sort out your layout, brother. Once I’m back in my home state I can look.
     
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  9. 8urchevy

    8urchevy Tele-Meister

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    No wor
    No worries. I am just elated the damn thing works and didn't create fireworks .lol . I hope to sort it out this weekend
     
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  10. Lynxtrap

    Lynxtrap Tele-Holic

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    Sounds like 120Hz hum and might be caused by bad grounding or problems with the filtering of the power supply. Your ground scheme is a bit unclear from the picture.
    You could try to pull one tube at a time starting from V1 and see if you can locate the problem that way.
    But if the hum is unaffected by the master volume, the problem probably lies in the PI or output stage or comes from the power supply.
     
    Last edited: Feb 15, 2019
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  11. flyswatter

    flyswatter Friend of Leo's

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    Another way, if you have an audio-video editing program (the most basic freeware will suffice), is record the sound of the amp and pair it with a still photo of the amp, then upload to YouTube.
     
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  12. 8urchevy

    8urchevy Tele-Meister

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    I was a dummy when I wired this up. I forgot that the pilot lights were right above my unshielded input. Problem solved with the hum. However, this thing is really tight and punchy. I think that I need to play with the negative feedback to help loosen this up. The transformers are from the PA that I used to convert this to a Bassman. Am I on the right path?
     
  13. Luthier Vandros

    Luthier Vandros Tele-Holic

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    Hey, glad you worked it out. That wiring style always impresses me. There’s something so raw, chest hairy, and organic about it. I can literally imagine the odor of it; like an old rusty battleship. And Lol @ your “surprised it worked” comment! I switched on my first build with a broomstick handle from behind a chair!

    If you want the sweetest and juiciest fender tone around, try to match the the plates to the AA964. But! If you still insist on having the lowly Bassman sound (jk!), there are some areas to play with.

    Investigate your voltages throughout. If your pt is supplying on spec for that 5f6a circuit and you still find it too stiff, you can loosen it up a bit by lowering first stage filtering a smidge, playing with preamp voltages, or getting yourself a lively, medium efficiency speaker.

    Yes, this least sexy option, and the one that doesn’t let you play with your soldering iron or enjoy the rich aroma of solder, can be the ticket to tuna town for you. After 20 years of building and modding, I’ve literally just stumbled across the importance of speaker selection for acquiring vintage fender tone. I’m a dense man at times and have seen this advice for decades.

    For context, I played lead guitar in a touring modern rock band and relied on overly efficient drivers with massive power handling to give me tight and saturated tones. My love of Phrygian shreddy things yielded to more organic blues-based noodley-feels and I decided to have a gear makeover. Out went the coliseum head and in came the blackface clone builds. No, I’ve never played a coliseum.

    Guess what can happen when you use speakers like these with vintage circuits? You can get stiff and lifeless tone - with no lively interaction and feel beneath the fingers. This sent me spinning off in the wrong direction for years.

    I took a chance on a Vibrolux clone a few months ago, but it came with a pair of high efficiency drivers. I was so disappointed with the stifff and lifeless feel. Very strident, as well. Then after more research, the advice I ignored or denied bubbled up. I took a gamble on a pair of low wattage/efficiency Webers and the cloud and haze of my own, decades old dumbassery lifted and lights from the heavens shone down. Angels wept. There it was. The tone and feel I always wanted and the actual feeling that the speakers were wired right to my fingertips. Transformative.

    Anyway I’m blabbering on. No sleep the last week. Congrats and huge props for diggging your heels in and doing the work. I’ve fallen victim to my own sloth many times, as I waited for answers to arrive instead of doing the work and actually learning.
     
    Last edited: Feb 16, 2019
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  14. Phrygian77

    Phrygian77 Tele-Afflicted

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    I didn't know you felt that way about me... lol

    Sent from my KIW-L24 using Tapatalk
     
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  15. 8urchevy

    8urchevy Tele-Meister

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    That advice is great and considering my speakers are Celestion 70/80 I am sure that is a huge part of my issue. It sounds fantastic clean, but very stiff when trying to dial in some gain for lead tones. That edge of break up sound is what I love the most and it just doesn't have it. Clean or crunch that's it. No inbetween. I do have some other speakers to try from an old solid state amp. If they blow I am not concerned lol.

    I did have one issue on the initial start up. After playing it for like 5 minutes the sound cut out. I of course went into panic mode at first, but quickly went to wiggle tubes to check for dirty connections even though I did try to clean them out during the build. As soon as I just wiggled the first tube a loud pop occured. I jumped a mile and quickly shut it off. My son started crying and I went to console him thinking a tube exploded and felt sorry.

    Little did I know the little **** blew a big balloon up too far and it exploded. Lol. Man my heart was racing. Perfect timing of touching tube and that balloon exploding sent me nearly into cardiac arrest.

    The actual problem was a broken pin inside the tube socket from me removing the old stuff off of it. I got too carried away with getting every last bit off the pins and the metal fatigued causing a break. Installed new socket and all is right with the world. :)
     
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  16. Luthier Vandros

    Luthier Vandros Tele-Holic

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    I just can’t quit you :D

    It’s funny how hypersensitive you can become when fooling around with lethal voltages lol. Messing with a reverb amp is like that, too. The slightest bump and you get that massive spring explosion sound.

    So, your clean tone is glorious. How do you feel about the character of the crunch tone aside from the stiffness? Is there any transition at all into overdrive?

    Reason I ask is because sometimes the change a different speaker brings is more related to a shift in the onset of overdrive relative to volume. Sooner or later breakup. Sometimes it’s the quality of the breakup itself. Jagged edges vs smooth mids.

    The bassman should have sone nice compression as it starts transitioning into od and that, coupled with the compression from the speakers (if it exists in your scenario), should give you the squish you are looking for.

    This is all speculation; your voltage measurements will speak volumes (honk honk!) about what’s going on. If you have time to compare against the original schematic and share, that would be helpful to those looking to help you adjust your tone. Bias, plate, screen, etc.

    Wait a minute - what’s the spec on your output transformer? Any idea what that old Bogen was putting out? I once built an ab763 clone using a spare 100w ot I had lying around. Clean was amazing, but thing was super stiff and the overdrive was very flat and dimensionless. I tweaked and tweaked the filtering and plate voltages for months. Then I stripped it down, modding the power amp to run at 35w with two tubes and smaller ot. Bingo!

    It was at that moment I realized the magic juju for me lied within the smaller ot (and lower plate voltages would be the second thing I’d come to discover much later on the journey).
     
    Last edited: Feb 17, 2019
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  17. 8urchevy

    8urchevy Tele-Meister

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    Lol. Yeah you definitely get in tune with what you are doing. I am a maintenance mechanic and electrician at a factory so high voltages I am quite familiar with, but if you want to stay alive you best have your crap in a pile so to speak.

    I am not certain of specs on either the pt or ot because I can't find much of anything on this particular MX30A model. The MX30 has info floating around the interwebs, but I don't want to assume that they share the same transformers. Considering that these were PA's it doesn't surprise me that the clean sounds great even thought the overall circuit has been changed. The ot is quite large and is multitapped. I do have a much smaller push-pull ot I may try out. I don't need high volumes as I don't play out.

    I haven't made a formal chart with voltages yet, but do plan on doing so and when I do I will post them for review. One thing you mentioned earlier was the first stage filter cap. When I ordered my can cap I got one that the value for that stage is 20uf instead of 8uf per the schematic. I did that because it was more affordable. I reckon if I can't manage to get what I am looking for I will order the 8uf.

    The other thing to note is that my pt doesn't have a bias wire so I cathode biased it. Honestly, I started the amp and let it idle for awhile looking at the power tubes for red plating. It didn't so I haven't checked the actual bias reading yet. I know I should have by now lol. I reckon that it may be a tad on the cold side. I certainly appreciate your responses. Thank you
     
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  18. Luthier Vandros

    Luthier Vandros Tele-Holic

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    Get those volts squared away! You may be in love after that. Then I’d look at the ot.

    Cheers!
     
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  19. peteb

    peteb Friend of Leo's

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    How is the over all volume?


    Does it get as loud as you think it should?
     
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  20. jrblue

    jrblue Tele-Afflicted

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    +1 on the OT suggestion; ditto on the speaker significance. Both can be transformative.
     
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